The concept of digital actuators is known, however generally such actuators are relatively complicated to machine and cannot easily be manufactured. Further, it is difficult to change the capacity of any one such actuator since normally all of the pistons and cylinders used to provide the digital action are incorporated in a single housing.
U.S. Pat. No. 4,602,481 issued Jul. 29, 1986 to Robinson discloses a linear double acting digital system and German Offenlegungsschriftde 3836103 A1 to Damler-Benz Aktiengesellschaft discloses an axially operable multi-piston and cavity arrangement for forming a digital actuator.